The Chediak-Higashi syndrome (CHS) is an autosomal recessive genetic disorder which occurs in man, mink, mice cattle, cats, and killer whales. The CHS is manifested by diluted oculocutaneous pigmentation, photophobia, increased susceptibility to infections, and abnormally long bleeding times. Greatly enlarged granules, including melanosomes and lysosomes, are present in many cell types. The basic biochemical defect is unknown. A thorough study of the CHS cat visual system will be accomplished through ophthalmoscopic and biomicroscopic examinations, observation of eye movements, light microscopic and electron microscopic examination of the eyes, histochemistry, and autoradiographic anatomic mapping of the optic neural projections. The size, shape, and distribution of melanin granules and their relationship to lysosomes, especially in the retinal pigment epithelium (RPE), will be of particular interest. These determinations will be made during histologic examination of a series of eyes from both normal and CHS kittens of increasing ages in order to catalog the developmental changes that occur in kitten eyes and to determine if the coalescence of melanin granules occurs post-natally in CHS kittens. Acid phosphatase histochemistry will be done to determine if lysosomes have fused with melanosomes. The eyes of old adult CHS cats will also be examined histologically and compared to those of kittens. The RPE of CHS animals will also be examined closely for evidence of impaired turnover of photoreceptor outer segments. These studies should serve to help clarify our understanding of the relationship between ocular melanosomes and lysosomes. They may also provide information regarding retinopathies due to impaired destruction of shed photoreceptor outer segments, as well as adding to our knowledge of RPE function. Autoradiographic tracing of optic nerve projections in CHS cats will be done to gain additional knowledge on the relationship of ocular melanin to nerve projections, and on the nervous system abnormalities associated with nystagmus. Gaining a thorough understanding of ocular abnormalities associated with CHS in cats may also provide insight into ways of correcting or partially alleviating visual problems suffered by children affected with CHS and other forms of ocular albinism.